左连接三个表，将名称字段组合成一列

Question

我们的数据库中有三种类型的用户。我们正在尝试生成报告。我可以把他们一起加入。但如果我这样做，我有三个名字和三个姓氏列。我如何将所有三种数据合并到一列中。

SELECT e_job.objId AS 'Job Number', e_student.Lastname, e_student.Name, e_teachers.Lastname, e_teachers.Name, e_supportStaff.Lastname, e_supportStaff.Name 
FROM e_job 
LEFT JOIN e_student ON e_job.jName = e_student.username 
LEFT JOIN e_teachers ON e_job.jName = e_teachers.username 
LEFT JOIN e_supportStaff ON e_job.jName = e_supportStaff.username WHERE jStatus != 2 && jStatus != 7 && jStatus != -1 

当前输出显示7列，每种类型的用户都有姓氏的第一个名字。

如何组合最后6列，以便所有名字都在1中，并且最后名称在另一个名称中。

------------------------------------- 
|Job Number |Last Name |Fist Name | 
|-----------|-----------|-----------| 
|1   |Doe  |John  | 
|2   |Test  |Test  | 
|3   |Test 2  |Test2  | 
------------------------------------- 

谢谢

Answer 1

一个通用的解决方案可能是一个联合查询是这样的：

SELECT e_job.objId AS "Job Number", e_student.Lastname AS "Job Number", e_student.Name AS "First Name" 
FROM e_job 
INNER JOIN e_student ON e_job.jName = e_student.username 

UNION 

SELECT e_job.objId AS 'Job Number', e_teachers.Lastname, e_teachers.Name 
FROM e_job 
INNER JOIN e_teachers ON e_job.jName = e_teachers.username 

UNION 

SELECT e_job.objId AS 'Job Number', e_supportStaff.Lastname, e_supportStaff.Name 
FROM e_job 
INNER JOIN e_supportStaff ON e_job.jName = e_supportStaff.username WHERE jStatus != 2 && jStatus != 7 && jStatus != -1 

注意左联接已改变为内部连接becase的我们就不再需要迎合其他表和内部连接，我们只获取具有匹配数据的行。

的选择，如果你想的类型的人之间进行区分，然后介绍了另一列，并更改使用UNION ALL

SELECT e_job.objId AS "Job Number", 'Student' as Type, e_student.Lastname AS "Job Number", e_student.Name AS "First Name" 
FROM e_job 
INNER JOIN e_student ON e_job.jName = e_student.username 

UNION ALL 

SELECT e_job.objId AS 'Job Number', 'Teacher' as Type, e_teachers.Lastname, e_teachers.Name 
FROM e_job 
INNER JOIN e_teachers ON e_job.jName = e_teachers.username 

UNION ALL 

SELECT e_job.objId AS 'Job Number', 'Support' as Type, e_supportStaff.Lastname, e_supportStaff.Name 
FROM e_job 
INNER JOIN e_supportStaff ON e_job.jName = e_supportStaff.username WHERE jStatus != 2 && jStatus != 7 && jStatus != -1 

注意：从 UNION，单独使用时，将删除重复的行结果（因此可能比UNION ALL慢，不会删除重复的行）。在我的第二个查询中，你不能复制3个子查询中的任何一行，因为第2列在每个子查询中都是不同的，UNION ALL是有意义的。